John XXIII and John Paul II canonisations to be broadcast live in cinemas 3D

500,000 people expected to turn out to see Pope John Paul II and Pope John XXIII be Canonised in the Vatican on Sunday.

April 27 will see the Canonisation of John XXIII and John Paul II in St Peter's Square in Rome.

Pope Francis is to perform the ceremony which is being called "a completely unprecedented event in the history of the Church" as four popes – Benedict XVI will also be present – are "symbolically united" for the first time.

The event has not been without controversy, however. Many have questioned the choice to canonise John Paul II just nine years after his death in April 2005, and the Vatican has been forced once again to defend the deceased Pope against allegations that he covered up and ignored sexual abuse scandals during his papacy, particularly those perpetrated by Marcial Maciel - founder of the Legion of Christ.

"There exists no sign of personal involvement of John Paul II in this case," postulator Mgr Slawomir Oder told a press conference at the Vatican on Tuesday.

"Of course in a 27-year long pontificate, there are going to be controversial issues, controversial appointments; people will always say, 'Oh he did not handle that well, I would have done it differently'," the Irish Times reports Mgr Oder as continuing.

"The point is no one is saying a pope is infallible in everything he does in his pontificate, nor that his possible mistakes represent a terrible mortal sin...the Church sees the saint as a great model, someone who bore witness to the Christian life in an outstanding way...but that does not mean that he was perfect in every single thing he did."

Around 500,000 people are expected to flock to St Peter's Square in person on Sunday, but for those who can't make the trip to Rome, Sky has picked up the rights to broadcast the ceremony in full both on Sky 3D and in 2D on Sky Arts in the UK, and on further channels across Europe.

Cinemas in Europe, the US and Latin America will also be holding special 3D screenings for movie-lovers to see the spectacular event on the big screen.

This will allow audiences around the world to feel "that they are actually there in St. Peter's Square, fully immersed in the event...in a way that would once have been unthinkable," organisers say.